Coal-retort lining



Maf., 3, 1925.

1,528,351 s. F. wALToN COAL RETORT yLINING Filed July ll 1921 Patented Mar. 3, 1925,

UNITED STATES PATENT oFFICE.

SAMUEL E. WALToN, 0E EoSToN, MASSACHUSETTS, ASS1GNoR,-EY MESNE ASSIGN- MENTS, To INTERNATIONAL COAL PRODUCTS CORPORATION, A coRPoRATIoN or VIRGINIA.

lCoAIfiaEToET LINING.

Appncann med July 11,

To all whom t may concern.' A

Beit known that I, SAMUEL F. WALToN, a citizen of the United States of America, and resident of Boston, in the county of Suffolk and State of Massachusetts, have invented new and useful Improvements'in CoalRetort Linings, of which the following is a specilication. y

This invention relates to retorts and more particularly to a lining for such retorts made of silicon carbide (commonly designated in the trade as carborundum, carbon, crystalon, etc.) The lining is applicable either to continuous or non-continuous retorts, that is, either` retorts in which the coal is fed through continuously or retorts in which the coal is charged andfired, and the residue removed before recharging, but it is particularly applicable to continuous retorts.

While silicon carbide possesses characteristics which are uniquely desirable in retort` linings t e use of the material for this purpose has never been satisfactory. For example, in continuous retorts where the c oal is fed through by means of va screw or equivalent means the outward; pressure exerted on the walls frequentlybreaks silicon carbide linings as heretofore constructed, which linings ordinarily have a cross-breaking strength or modulus of rupture of 2000 to 2200 pounds per square inch or less at 10000 C. Moreover, prio silicon carbide linings have been susceptib e to the action of the vapors or gases reduced in coal distillation as a result of which the linings have disintegrated in spots. And even though the fracture or disintegration is confined to a small region it necessitates cooling and emptying the entire retort, and this consumes much time and large expense.

The principal objects of the present invention are to provide a'silicon carbide lining for coal retorts and the like which has a high modulus of rupture at high temperatures and which will withstand the action of hot coal gases and other destructive substances. Corollarial objects are to provide-a silicon carbide lining which is thoroughly vitriied throughout and which will retain its strength and inertness throughout a range of temperatures above the tempera-l ture at which the bond vitrifies.

H1921. serial No. 483,743. 4

The Subject-matterof the invention is stituted of substantially dust-free silicon characterized as follows: The lining is concarbide grains bonded together with a semirefractory clay which is completely vitrified. The sihcon carbide grains are preferably of the random sizes produced by crushing in so the ordinary pan mills or of such sizes that the space not occupied by the grains is ap- The clay has a vitrication range at least of the order of 100O` C. and preferably as high 'as 150 C. That isthe bond will withstand a temperature of 100to 150 higher than the temperature at which vitriication begms.

With these characteristics the lining has-a modulus of rupture at least of the order of twice that of the prior products above referred to and frequently the lining will withstand Cross-breaking strains up to 5000 pounds per Square inch, at a temperature of 1000 C. Moreover the lining 1s substantially inert to the action of the substances with which it comes in contact in coal distillation so that costly shut-downs for lining repairs is practically eliminated. By providing a wide vitriication range the lining will withstand temperatures in excess of the vitrifcation temperature, thereby enabling" the material to be fired at a lower temperature than that at which it is to. be subjected in use and providing a wide safety factor in respect to the retort tem eratures. Moreover, the lining may be on y partially vitriied in the process of` manufacture, namely to the point where the bond has Set and partially vitrified, and then completely vitried in the normal operation of .the retort, .thereby reducing the time and cost of manufacture. The finished product is free from 1 the dark central core frequently displayed by prior silicon carbide refractory linin and to this I attribute a part of `its unlformly great strength.

Another factor contributing to the strength of the roduct is the dust-free character of the grains, since I have discovered that the strength is seriously diminished by the surface graphite and other dust always present in crushed silicon carbide for the following reasons. First, because the strength of the product depends in large part on the completeness with which the indivi-dual grains are wet with the bonding materiahtand the dust which coats and surrounds the grains prevents the fused bonding material from coming into intimate contact with the grains and adhering thereto. Second, because the voids are so smallwhen the powdered graphite and dust are present, that they will not hold suflicient bonding material to make a strong product without forcing the grains of silicon carbide apart, which results in spaces filled with the bonding material and dust; a thick body of ceramic lbond forms a much less strong union between the silicon carbide grains than a thin film.A One way of eliminating the dust is mentioned hereinafter. l

r The clay should be plastic and smooth working. It should show partial viti-ification at or about 1250 and should develop a dense vitrified mass'at or about 1350 C. but should show no porosity due to evolution of gas at or about 1450", that is., after apparent complete vitrilication it should show vsubstantially the same density over a temperature range of about 100 C. This clay may be fired at a temperature of 1300 C, to 1350 C. although intended for use at a tempera-ture of 100 C. to 150 C. in excess of this.

In order to illustrate the'nature of the -invention and its application I havev shown one concrete embodiment thereof. in the accompanying drawings in which,

Figure 1 is a diagram showing the general arrangement of one type of continuous retort; Figure 2 is a transverse section of lthe retort lining; and l Figure 3 is a perspective View of a typical element of the retort.

The particular application of the inver/1- tion chosen for the purpose of illustration comprises a retort chamber 1, revolving axles 2 extending along the axes of the chamber and Fig. 2) vand driven by Imeans not shown, thel axles carrying oblique vanes 3 for feeding the coal Vthrough the chamber, and means 4 for feeding the coal into the chamber, the chamber having an youtlet 5 for discharging the residue.

The lining for the retort, shown in Fig. 2, preferably comprises a plurality of sections 6 of the general shape shown in Fig. 3.

These sections have flanges 7 extending circumferentially of the retort to space the lining from the walls of the retort, the circumferential channels formed by the flanges constituting ilues for the application of heat to the retort. The linin sections are also preferably provided wit grooves 9 .so that theyinterfit.'

In order more clearly to instruct how to produce the lining herein claimed I will now describe in detail one concrete procediire.

Crude silicon carbide as obtained from the electric furnace is crushed in a pan mill and passed over a 16 mesh grid. The product of the pan mill contains granular silicon carbide particles of random sizes, the upper limit of size being determined by the aperture of the grid. In addition yto the silicon carbide ains-the product contains silicon carbide our, graphite, and other dust. The pan mill material is next thoroughly washed to remove foreign'dust, graphite and such part of the silicon carbide as will readily iioatl off under the conditions of energetic washing, with steam or air agitation, without undue loss of the desirable sizes of grain. The silicon carbide removed ranges from tongues j 8 and a few per cent. of the 100 mesh to 95 to 99 l per cent. of the almost impalpable powder or ii'our such as would float in water for many minutes, but if approximately 95 per most purposes.

The washed mass of silicon carbide grains may be dried or the/amfumt of water contained in it may be takerrnto` account in adding water to mix with the bond.

I next mix the silicon carbide grains as above prepared with a certain amount of semi-refractoryl clay, temporary binder and Water. The amount of clay used is of great importance.- '.Io determine the correct amount Iv first determine the percentage .of voids or interstitial space in a carefully selected average sample of the silicon carbide to be used. This may vary from 25 to 35 per cent. depending upon the crystalline character of the particular furnace run of silicon carbide used, upon its purity', upon and upon the extent to which washing has been carried on. I use an amount of clay equlvalent 1n dry volume to 85 per cent. of

.the free or void space in the 'sample of siliythe-condition and operation of the pan mill portions indicated, the following clays:

Albany slip clay, approximately 15 per cent.; Kentucky ball clay, approximately 65 per cent.; Georgia plastic kaolin, approximately 20 per cent.

vThe articles prepared as above described are next dried so that they vcan be handled and are then loaded into the kiln in the usual manner and burned. The firing 0peration is carried on to such a point that every portion of every article reaches the vitriication range of temperatures and re- `mainsin this range of temperatures long enough to insure complete and homogeneous vitrification, which is very important. Owing to the long vitriiication range ofthe clay used it is possible to use so high a kiln temperature as to insure complete vitriication Without danger of overheating and spoiling any part or' the material.

The product obtained by the above procedure shows a modulus ot rupture as high as 5000 pounds per square inch at 1-000 C. and averages Well up to 4000 pounds. Its thermal conductivity is from 10 to-20 per cent. higher than that of the hitherto available commercial articles. It is remarkably impervious to gases. In commercial service in coal retorts it has stood up over long periods Where silicon carbide products made by the hitherto knownl processes have failed. I have found the use of a grain of the random sizes produced by crushing, and particularly by` pan mill crushing, to give the maximum, strength of product. The use of screened or sized grain, either Wholly as a mixture of selected sizes or as an addition to pan mill material, gives no increase 'in strength, and usually a marked decrease; and the use of such sized grain is very expensive. Where unsalable sizes of grain are available they may be disposed oi Within reasonable limits by addition to the random size crushed material; but tue use of a mixture of standard sized grains alone'is unsatisfactory, unless the remixing be, in fact and substantially, a reconstituting of the original random size` bythe compounding ot all, or nearly all, of the sizes derived therefrom by screening, and in, or nearly in, the ratios by Weight of the sizes so derived.

The shaping of the mass of silicon carbide, clay, `Water and binder can be carried out by any of the Well-known methods such as hydraulic pressing. hand tampingg machine tamping, etc. I have found that careiul hand tamping gives excellent results but any carelessness results in a weakened product, and if dependable labor is not available hydraulic pressing or machine tamping is advisable.

Instead of completely vitrifying the bond prior to its installation in the retort it may be only partially vitriied to the extent of rendering it self-supporting and then completely vitriied in the first operation of the retort.

I claim: l. A lining for a retort comprising substantially dust-free silicon carbide grains bonded together with a 'vitried semi-refractory clay, the dry volume of which before bonding is of a minimum 75% lof the space not occupied by said grains and of a maximum substantially equal to said space in volume.

2. A lining for a retort comprising substantially dust-free random-sized silicon-carbide grains bonded together with a vitriied semi-refractory clay, the dry volume of which before vitrificaton isapproximately seven-eighths of the space not occupied by the grains.

3. A lining for a retort comprising silicon-carbide grains of such sizes that the space not occupied by the grains is of the `order of 25 to 35 per cent. of the total volume, the grains being bonded with vitrified semi-refractory clay, the dry volume of which before vitriiicatio'n is not less than 75 per cent. of said space nor substantially greater than said space.

1 4." A lining for a retort comprising substantially dust-free random-sized siliconcarbide grains having such a size range. that the space not occupied by the grains is approximately one-fourth of the total volume, the grains being bonded With-vitriied semirefractory clay, the dry volume of which before .vitrilication is approximately seveneighths of said space.

5. A lining for a retort eomprisin 'substantially dust-free random-sized slliconcarbide grains having such a size range that the space not occupied by the grains is approximately one-fourth of the `total volume, the grains being bonded with vitriiied semirefractory clay, the dry volume of which be'- fore vitriication is approximately sevenleighths of said space, and the vitritication range of which is at least of the order of 100 C. y

Signed by me at Boston, Massachusetts. this 8th day of July, 1921.

SAMUEL F. WALTON. 

